Iranian Supreme National Security Council Secretary and chief nuclear negotiator Saeed Jalili smiles before talks in Almaty, Kazakhstan, Tuesday. World powers began talks with Iran on its nuclear program on Tuesday, in a fresh attempt to resolve a decade-old standoff that threatens the Middle East with a new war.

Almaty, Kazakhstan — Iran and six world powers have today broken an eight-month dry spell, sitting down to top-level negotiations over Iran's nuclear program, despite low expectations and much to do.

Iran is being presented with a "real and serious and substantive" revised proposal to curb its nuclear advances, say diplomats of the so-called P5+1 group (the United States, Russia, China, Britain, France, and Germany).

While the updated offer is expected for the first time to include modest relief from sanctions that have crippled Iran's economy, it also requires Iran to take substantial first steps to halt the most prized and sensitive elements of its nuclear program. Iran rejected that offer last spring.

Both sides accuse the other of being unwilling to engage in a balanced, step-by-step, and reciprocal process, and of making unreasonable demands. That tension – and fear of being portrayed as a "loser" in any deal – has complicated past chances to move forward.

“The onus is very much on the Iranians,” said Michael Mann, the spokesman for European Union foreign-policy chief Catherine Ashton, who leads negotiations for the P5+1, as talks were under way.

“Iran needs to understand that there is an urgent need to make concrete and tangible progress," Mr. Mann said, speaking earlier. While the "good and updated offer" is "responsive to Iranian ideas," he added, it is "based upon what we put on the table before."

Iranian sources said they had also prepared their own counterproposal, and had several different versions ready to fit what the P5+1 laid down.

“It’s something that will balance their [P5+1] offer,” said an Iranian source close to the talks.

The two-day negotiations in the snowy and fogbound Central Asian city of Almaty, Kazakhstan, come as Iran has stepped up its rhetorical defiance of the process.

Iran's supreme leader, Ayatollah Ali Khamenei, on Feb. 16 was dismissive of diplomacy conducted while Iran is being targeted by ever-increasing sanctions, and has been stung by a covert war that has included assassinations of Iran's nuclear scientists and malicious computer viruses.

"Negotiations mean that we should accept what they say and surrender so that they lift the sanctions," said Mr. Khamenei, according to a transcript published on his website. "If the Iranian nation wanted to surrender, they would not have carried out a revolution" in 1979, which toppled the pro-West Shah.

Iran could be a "reasonable" partner in talks, Khamenei said, "if the Americans show that they will not bully us anymore, if they show that they will not commit evil deeds, if they show that they will not say and do irrational things, if they show that they will respect the rights of the Iranian nation...."

In Almaty, the Iranian source said: "Things will not get worse for us; we are already subjected to the hardest sanctions but have been able to overcome these problems."

What's on the table

The key issues on the table in Almaty mirror those at three previous rounds of talks that failed to yield a breakthrough last spring in Istanbul, Turkey; Baghdad; and Moscow.

The P5+1 demands that Iran permanently halt all enrichment of uranium to 20 percent purity – a medium level used to fuel a research reactor in Tehran, but which is just a few technical steps away from the 90 percent that can be used for weapons.

The P5+1 also wants Iran to close a deeply buried enrichment facility at Fordow – which is currently under United Nations inspection, but is also largely impregnable to Israeli and US air attack – and to remove it from Iran.

"We are trying to outline as well a pathway for sanctions relief," a senior US official said on the eve of the talks. "All things are possible. All of the objectives that Iran seeks to meet can be met."

Pick up the tempo

The "real message" of the Almaty meeting, says the US diplomat, "is for Iran to understand and to appreciate that there is a path forward for them to get the relief they're seeking and to have a peaceful nuclear program.”

The US wants to create "momentum to these talks" and will pursue a quicker tempo of meetings, adds the diplomat, including perhaps a technical meeting in the coming three weeks, before Iran's long Nowruz New Year holiday.

Iran, for its part, demands that its "right" to enrich uranium be recognized, as a signatory to the Nuclear Non-Proliferation Treaty. It also wants far-ranging sanctions, whose targets have included critical oil exports and central bank transactions, to be lifted in exchange for Iranian concessions.

But Iranian politicians in recent weeks have also stated that they will "never" close Fordow. And a letter signed by 250 Iranian parliamentarians on Sunday called on Russia and China "not to follow the US's illogical demands" in talks. The MPs asked the US and P5+1 to "accept the nuclear realities" because "Iran's nuclear train within peaceful goals will never stop."

Iran over the weekend announced that it had plans to build 16 more nuclear reactors – in addition to the delay-plagued Bushehr reactor recently completed by Russia. It also announced that more discoveries of natural uranium have allowed it to nearly triple estimates of its reserves.

A Feb. 21 report by the UN's International Atomic Energy Agency (IAEA) noted that Iran had increased the number of installed centrifuges by nearly 25 percent in the previous three months, to 12,669, and had begun to install a newer, more efficient model.

The IAEA also noted, however, that Iran had resumed conversion of its 20 percent stockpile to an oxide form for nuclear fuel, rendering it much more difficult to be used in any push for a nuclear weapon.

Putting more on the table for negotiations

"There's no question ... that some of this [Iranian] action is also to put more chips on the table in a negotiation, and it meets both [Iran's] desire to move their program forward as well as to be in a stronger negotiating position," says the US official.

If Iran does not accede to P5+1 demands, "there will be continued pressure and continued sanctions enforcement," the US diplomat adds. "It's an ongoing process of additional designations, additional closing of loopholes. There are other areas where pressure can be put on."

The diplomat says the revised deal includes "some steps in the sanctions arena, perhaps not in the fundamental ways ... that Iran is looking for."

That might include recently imposed restrictions on Iranian dealings in gold and precious metals – the latest measure imposed by the US on Feb. 6 – to skirt restrictions for oil purchases.

Iranian officials have said already that would not be enough. A further factor that may make a deal for Iran less likely are presidential elections in June – the first since weeks of violence followed the last contested presidential vote in 2009.

"If they want constructive negotiations, it's better this time they come with a new strategy and credible proposals," Iran's nuclear negotiator, Saeed Jalili, said over the weekend. He added that the new offer should be one that "lacks the previous mistakes."

How much leeway?

As the talks began, it was not clear how much leeway Western officials might have to ease sanctions – which also include four sets imposed by the UN Security Council – as a lever in the talks.

Though imposed over the years primarily to change Iran's nuclear calculus, sanctions have yet to do so, and removing them will not be such an easy incentive to offer, states a report released on Monday by the International Crisis Group (ICG).

"Sanctions have become so extensive and so intricately woven that it will be hard to offer significant, concrete relief [to Iran] short of a major – and improbable – turnaround in major aspects of the Islamic Republic's domestic and foreign policies," reports the ICG. "Reaching the threshold for removing US sanctions in particular is hard to imagine."

In his Feb. 16 speech, Khamenei said any promise to lift sanctions "is a lie ... to make the people of Iran eager to negotiate."

Iran's top authority also repeated that Iran is not pursuing an atomic bomb.

"We do not want to build nuclear weapons and this is not because this will upset America, rather it is because of our beliefs," said Khamenei, adding that it was a "crime against humanity" to manufacture them: "This is our belief. It has nothing to do with you [Americans]."